No expense was spared for the Mach V: Its 3.2-GHz processor is overclocked by 800 MHz, and the machine packs three Nvidia GeForce GTX 280 cards running together for screaming performance. While media files live on the 1-TB hard drive, programs have their own pair of 64-gig solid-state drives. That way, when the CPU comes knocking, it reaps the benefit of the SSDs' read and write speed.
HP Blackbird 002 Exhilaration 
$6,311 
Sturdy case with a pedestal for quiet airflow. Needs faster graphics cards.
Alienware Area-51 ALX $8,780 
Uses a pair of efficient ATI Radeon HD 4870 X2 cards that placed third in speed tests. Plastic and aluminum case is chintzy.
Uberclok Reactor $4,300
Cheapest tested. Ran Crysis without making it look like a flip book, but stuttered a bit.